Why weigh bullets?

  • Last Post 30 September 2010
CB posted this 21 June 2007

(this thing is getting too messy, I can't find things. I'm going to start new topics as needed.)

Why I weigh cast bullets.


A. Weighing allows me to eliminate “strangers". My average lot size over some 14620 cast bullets weighed and recorded is 107. This does not include the “strangers", those bullets that weigh more than a half a grain away from the mean. I generally find 1-3 of these. I assume that these strangers will shoot less accurately.

B. Weighing allows me to segregate or class bullets. I shoot sets of 25 shots, every set is an experiment. I need sets of 25 bullets plus 1-2 in case I drop one. After weighing it is easy to select these sets of bullets with little or no weight variation within each set.

C. Weighing allows me to understand better what is going on during casting. For example, I had suspected trouble with a lot of 25:1 that I bought, and had been casting with a mixture of lead and a little foundry type. After each lot I added lead to the pot, wanting softer bullets. Each lot had the average weight increase. This lot has an average of 183.6 grains, and a standard deviation of .171 grains.(183.3-184.0 only.) There's not enough ?tin?, certainly not enough something, because the quality of the bullets has gone down based on the variation and the appearance. There are many other lessons I've learned by weighing bullets.

D. Weighing allowed me to calculate and record the average weight and standard deviation of weight of each lot of bullets cast; and this data leads me to this conclusion: After eliminating “strangers", the standard deviation of bullet weights, on average, for >14000 bullets, is .151 grains-and this includes some very messy results. Then it is reasonable to say that under proper conditions a caster should be able to cast bullets that weigh +/-.5 grains virtually every time, and with culling, lots of bullets can be held to +/- .3 grains easily. ( I suspect that variation is not a function of average bullet weight, but don't know, yet.)


Does weighing cast bullets matter?

Based on the results of the testing performed with round-filed bullets in 2007, it appears that pretty big holes or bubbles in cast bullets have a pretty small effect on accuracy.

In the arena where average five shot group size at 100 yards is 2” or greater, weighing bullets may not matter.

Where average five shot group size at 100 yards is <2", it MAY be true that careful inspection, weighing, culling and segregation substantially reduce group size.

It has often been stated that with average group sizes well under 1", that weight variation within the feasible range increases group size substantially. However, data to support this belief is sorely lacking, and needed.


Why does cast bullet weight vary?

This is what I think, not what I know.

Bullet weights from the same pot of alloy vary, at least mine do, even after visual inspection and culling under a 4X lighted magnifier.

I think that there are only a few causes of this weight variation.

First is holes or bubbles in the bullet, not visible during inspection.

Second is “incomplete fill out” or rounding of some edges, slight enough to be missed during inspection.

Third is due to variation in weight due to variation in diameter/shape due to variation of the pressure with which the mold is held closed.

I think that weight variation due to alloy composition is ruled out because of the “same pot of alloy” condition.

joe brennan

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Tight Wad posted this 30 September 2010


let me weigh in on this topic,ha ha.  I shoot Sierra BTHP 180 grain Match Kings, My gun shoots these best of all. My Hyskore gun rest with remote trigger can shoot a .605 inch group of these bullets at 100 yards summer, winter, rain, or shine. Do not show up to a local gun range with money to bet and I have a box of these in my range bag. It started out that I shopped at Sierra because I live in Missouri and believe in Patronizing business that are (first to last) in my Neighborhood, City, County, State, and Country. Sierra is located 50 miles from Kansas City in a small town named Sedalia MO. The state fair is held in Sedalia which has given me an opportunity to drop by their facility. Sierra is home to the largest underground privately owned testing facility in the world 300 yards. One of the many tests that are conducted on their bullets, before they are offered for sale is taking 5 random bullets from a batch and shooting them at target set at 200 yards.  The total group cannot exceed .625 of an inch. It appears all their bullets go through the same hole at 100 yards and this is  not considered a sufficient quality examination. I write all of this to make one point, if you want to construct an accurate bullet and find out what is important and what is not, ask some one who has done it. Sierra bullet weight control tolerances are +/- 0.3 Grains. It appears varying weights start showing up at long distances, when the energy starts bleeding off.  The shorter the distance the more power, the less the difference.  if you were to take two bullets weighing 20 grains different and everything else being exactly the same, then firing them from the same gun there is a distance that both bullets will go through the same hole, say 25 yards, but the lighter bullet will travel farther being propelled faster, and maintain a higher trajectory than the heavier slower bullet.  20 grains or .5 grains the heavier slower bullet always hits the ground first, this is just physics.   I full well realize some who read this are not ready for this information, and will want to argue, on the other hand there are some nodding their heads right now, if you are nodding your head here is another revelation, Sierra polishes their bullets too.  Smart people learn from their mistakes, truly intelligent people learn from others mistakes.

Some People Invest in Gold & Silver, I Buy Lead & Brass/Steven C. Johnson

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Dollar Bill posted this 24 November 2009

tturner53 wrote: Those tiny weight variations you guys get amaze me. I think I must need to flux more. I'm with ya, Tim. Until a year or so ago, I only had one casting pot, a Lee 10#. Since I started alloying in the fish fryer and casting from a dedicated pot, my consistancy has improved. Still not where I want to be. Out of 100 bullets, after rejecting visual defects, I still get a 1.5 to 2 gn differential, and I think that is from garbage still in the alloy. I've got a couple hundred #s of WW in ingots, so I'm going to add some tin and flux like crazy before I pour that into ingots. See if that helps.

It's like everything else in this sport. All I try to do is better what I did last time, whether it's in the initial melt stage or on the firing line. Do a little better each time.

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tturner53 posted this 23 November 2009

Those tiny weight variations you guys get amaze me. I think I must need to flux more, I can see a little crap in some of my bullets. Typical for me from a two cavity mould is +/- up to 2 gr. on a 200 gr. bullet. Probably need to clean my pot(no, not that pot). Still, getting better all the time. I wonder if when I can get consistent sub-moa will I be content? Or maybe just keep chasing smaller groups? If I recall correctly, the record is .2 something. Fine line between mediocrity and fame. I suspect eventually 100 yd. groups will be meaningless due to inability to measure a difference between competitors. Like Olympic records measured in thousandths of a second.

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LWesthoff posted this 23 November 2009

Bob: Good hypothetical question, but...I cast .30 cal. bullets for match competition - all three styles around 200 gr., and I select bullets from the top of the bell curve, with a maximum weight deviation of +/- 0.2 gr. More often it's a total weight spread of 0.3 gr. That's a maximum weight variation of +/- 0.1%. Applied to your 500 gr. .45 bullet that would be a total weight variation of one half grain. With your 50 gr. mouse killer, it would be too small for me to worry about, but the point I'm trying to make (not very well, I'm afraid) is that a 2% weight variation is far too great to even consider - regardless of the “target” bullet weight. Frank Marshall, in the article I referred to above, was talking about the difference in obtainable accuracy between targets shot with bullets varying 0.1 grain and those shot with bullets varying 0.2 gr., and he makes a good argument - IF you are trying to shoot one hole groups. If you are trying to develop a good hunting load, or a good plinking load, or even a good cast bullet silhouette load, then I think there are a lot of other considerations that enter into the picture. If that's what I was after, I'd still weigh my bullets, but I probably wouldn't be quite so picky.


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Bob Krack posted this 23 November 2009

Lots of good logic here.

The one thing that confuses me is this - 'spose I cast a 500 grain .45 and another of 510 grains, I am lookin' at a 2% difference I think.

Now I cast a 50 grain .22 and a 51 grain I still think I'm lookin' at a 2% difference.

So - if we do decide that weight has an effect, why would I choose .5 grain per projectile difference as the determining factor? Why not 1% or 1/4 % or 2 % (independent of the total weight)?

That is not even considering the difference in speed or rotation rate (twist).

Can anyone here tell me that a 2 or 3 or more percentage difference in weight has absolutely no effect on the accuracy of the projectile?


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big boar posted this 19 November 2009

Though I do shoot from a bench sometimes, I wouldn't consider myself a benchrest shooter. Most of my shooting from the bench is to work up, compare or verify a load. I've done the visual/weighing of batches of bullets over the years as we all have and divide them into lots of A(best) or B(minor defect/weight variations). I've surprized myself a couple of times when, shooting groups from the B lot, has given superior or equal target results. This is usually defects of rounded bases and targets were limited to 50-100yds. When I shoot 200yds I've only ever shot groups from A-best lot. Perhaps this is an unfair test but I now toss out fewer defective bullets and for anything out to 100yds I think I'm ok.

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Dollar Bill posted this 19 November 2009

LWesthoff wrote: Haven't any of you guys ever read Frank Marshall's article titled “ORIENTATION AND SELECTION: TWO KEYS TO ACCURACY” on page 140 of the NRA Cast Bullet Handbook? I have. It's why I orient components. I know I can't produce perfect bullets so it just makes sense to me to index everything, for match loads, to minimize the effects of the imperfections.

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RicinYakima posted this 19 November 2009


No, it is not logical to assume a 1% weight variation will make a 1% larger group. If a void, it depends upon where that light spot is in the total volume of the bullet. Farther from the center line of form, increase instability.


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tturner53 posted this 19 November 2009

Just a thought; would it be logical to assume a 1% weight variation would cause a 1% variation in group size? For instance, a 1” group would become 1 1/100” group? Speaking of Frank Marshall, I've been reading a bunch of his old FS articles, that guy is somethin' else. I gotta get that CD. You guys wanna treat yourself to a good time, order some old Fouling Shots. This may be a little corny, but when I'm reading them I get the feeling like I'm...well, I'll stop there, I don't want to make you all cry. I'll just say it's special, makes me realize how much more there is to the CBA than meets the eye.

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LWesthoff posted this 19 November 2009

Haven't any of you guys ever read Frank Marshall's article titled “ORIENTATION AND SELECTION: TWO KEYS TO ACCURACY” on page 140 of the NRA Cast Bullet Handbook? Marshall makes a pretty darn good case for weighing bullets for use in competition, and has some (composite) targets made with bullets of various weight spreads to back up his argument. Makes sense to me. I weigh every bullet I cast that survives my initial visual check, and I segregate by weight.

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billwnr posted this 18 November 2009

RicinYakima wrote: If you are weighting them anyway, for internal flaws, why would you not drop them into separate cups of 0.1 grains? Bingo!!

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RicinYakima posted this 18 November 2009

If you are weighting them anyway, for internal flaws, why would you not drop them into separate cups of 0.1 grains?

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Dicko posted this 18 November 2009

I agree with Pat i's point that very few can show evidence that weight variance affects acuracy, and what seems logical is accepted as fact without proof.   That's not to say that weight might not affect matters, but slight weight variance shares with slight powder charge variance the distinction of being the least important factor.

You'd need a significant weight variance to see it on target and then only at long range.   Some primers vary chamber pressure quite a lot, and because pressure is closely related to MV it would cause significant variance in MV which would have a much bigger effect on grouping than slight difference in bullet weight.  Same goes for case weight, so if you want to weigh anything, weigh your cases.

Of course it depends what is meant by “accurate” and how much variance in bullet weight is acceptable.   It also depends on the rifle.   Walt Berger once told me that the difference between a hunting bullet and a bench rest bullet could hardly be detected in a sporting rifle because even an accurised sporter is not accurate enough to take advantage of the quality of bench rest bullets.

So, slight variance of maybe half a grain will not show up in sporters but it might in a heavy bench rest rifle.   But then all the other factors will have been taken care of as well.   It amounts to eliminating the variables.   And that is one of the only two reasons for weighing bullets, the other being that its the only way to find those with air bubbles.

But I have news about weight variance from the same melt.   First, you'll get bigger variance from two cavities than one because of tolerances.   Second, my rifle bullets are seldom outside 0.20 grains either side of average.   Third, random weighing rarely finds a bullet outside those limits.

As for mould temperature affecting weight, I very much doubt it.   Or alloy hauled out from different depths of the pot.   But I will run a test at two significantly different temperatures with a single cavity mould and see what I get.

Bottom line ?   Weighing is probably a good idea for a match to cull out the odd flyer that might be light because of an air bubble, but otherwise bullet weight and powder charge weight are the least important factors in accuracy.   Within reasonable limits.  Reasonable would be half a grain each way, which should be easy to get with proper casting technique.  
















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codarnall posted this 30 October 2009

It's my opinion only but I tend to thing impurities in the melt give rise to most inclusions when the temperature, hot mold everything else seems normal.----Charlie

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mrbill2 posted this 27 October 2009

Somewhere on this computer while just surfing I seen a picture of a set up where the mold is vibrated while being poored. Don't know if that would reduce the voids or not.


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Dollar Bill posted this 27 October 2009

That brings to mind a post by Ed Harris. He had sectioned bullets from a top competitor and found they all had tiny air bubbles, but were all close to the longitudinal axis, so had little effect on the bullet flight. Until (or if) my casting technique improves to the point I can produce such bullets, it would seem advantageous to orient components.

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RicinYakima posted this 27 October 2009

Vaughn's book is required reading for an update on Mann's work. It has been a couple of years since anyone has asked, for the new members, what reading list they should be working on.


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codarnall posted this 26 October 2009

Joe Brennan wrote: It has often been stated that with average group sizes well under 1", that weight variation within the feasible range increases group size substantially. However, data to support this belief is sorely lacking, and needed.  

joe brennan Very nice essay!

Actually there are scientific experiments that test the dispersion of voids created at the cg of the bullet. 270 bullets were drilled at the cg with a .00118” drill.  Four three shot groups were shot a 100 yards from the lab test gun.  The bullets were orientated up down left and right  when exiting the barrel.  The four groups all under 1/2” are at 12, 3, 6, and  9'oclock on a circle five  inches in diameter in agreement with Dr. Franklin Mann 's equation published in 1909.   Canting can be bad bad too!----Charlie

Source: "RIFLE ACCURACY FACTS", by Harold R. Vaughn  (Hal)

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corerf posted this 26 October 2009

I have found that by weighing, regardless of accuracy benefit, that I dont have to look as close to find those voids or round edges. The scale picks 'em out. Thats a pretty big void there. Is that Lyman 210 gr?

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Dollar Bill posted this 26 October 2009

That's why I weigh bullets. When visually inspecting hundreds of bullets, it's too easy to miss something like that. I find the weight inspection more revealing than the visual. We're talking rifle bullets. Weigh them, lay 'em out on a piece of cardboard in rows by weight, and you eventually end up with some sort of bell curve. Drop the high and low end for foulers, shoot the rest for record. With digital scales, it's too easy.

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